range-group

A RangeGroup is a data structure that holds a collection of one-dimensional ranges. It has builtin support for integers, reals/floats, dates, unicode characters, and unicode strings. You can also create your own Range type to integrate your own data types. It supports both inclusive (closed) and exclusive (open) range bounds. It has a comprehensive API for operations, such as searching, set operations (like union or intersection), filtering, random sampling, and more. It supports interpolation search for O(log(log(N))) membership tests and O(N*log(log(M))) set operations. It can also fallback to binary search for similar log(N) bounds.

Internally, it is storing a sorted, non-intersecting list of ranges. In many cases, it will give you better memory usage and more efficient set operations over the builtin Set type.

API documentation | npm package | GitHub source code

Installation

npm i range-group

This project uses ES 2015+ class features. A Babel transpiled and minified version is provided as rangegroup.compat.min.js, with exports under RangeGroup; though I highly recommend building a bundle yourself to customize the target and reduce code size. A plain minified version is provided as rangegroup.min.js.

The builtin range types, like IntType or DateType, are tree-shakeable. Feel free to submit a pull request to include another general purpose types you've made.

Quickstart

Take a look at the API for more comprehensive class and method documentation.

import { RangeGroup, ComparisonModes, IntType, RealType, ... } from "range-group";

If not using a bundler, you'll need to import from the minified version, which is pre-bundled.

A simple example:

const group = new RangeGroup([0,5], {type:IntType});
group.has(5); // true
group.subtract([3,6]);
group.ranges; // [{start:0,end:3,endExcl:true}]

Most of the methods on RangeGroup require the group to be normalized (exceptions being things like copy, filter, isEmpty, etc). This means the ranges are sorted and non-intersecting. The sort and selfUnion methods can do this, or the normalize method which calls these. You can also pass a normalize flag to the constructor:

const group = new RangeGroup(
	// also demonstrating another syntax for specifying the initial ranges
	[{start:-2,end:-5}, {start:4,end:8}, {start:3,end:10}, {start:11,end:16}],
	{type: IntType, normalize: true}
);
group.ranges; // [{start: 3, end: 16}]

Note the first range was removed, since its end came before its start (IntType uses ascending order). Additionally, the last two ranges were merged as there are no integers between 10 and 11. These behaviors result from the implementation of IntType.compare.

The RangeGroup.diff method is the most powerful, and most operations are implemented as calls to it. It can give you the difference between two groups:

const a = new RangeGroup([0,7], {type:IntType});
const b = new RangeGroup([3,10], {type:IntType});
const diff = a.diff(b, {copy:true, track_sources:true, self_union:false});
console.log(diff.ranges);
/* [
	 {start:0, end:3, endExcl:true, a:0, b:null},
	 {start:3, end:7, a:0, b:0},
	 {start:7, end:10, startExcl:true, a:null, b:0},
   ]
*/

See how filtering these results can give you the various set operations. This is supported with the filter option. For this and other options, logic has been added to optimize the work performed.

Setting self_union=false keeps the classified ranges separate rather than merging them automatically. If later you want to perform additional diff operations, you'll need to put it into normalized form by calling selfUnion (or normalize, though it will perform an extra unnecessary sort).

A Sampler class has been added which can randomly sample from a RangeGroup. For this to be efficient, it caches a cumulative summation on creation for use with binary search. If you want to update the RangeGroup, you'll need to create another Sampler:

const group = new RangeGroup([[0,5],[10,15]], {type:IntType});
const sampler = new Sampler(group);
// uniform sample
sampler.sample();
// non-uniform sample
sampler.sample(my_distribution()); 
// percentile function
sampler.sample(.2); 

Builtin Types

A RangeGroup needs to be passed a RangeType object, which acts as interface between your Range type and the methods inside RangeGroup. You can set a default type by changing RangeGroup.default_type. The following builtin types are available:

Ones marked with an asterisk/* also support a Norm type, e.g. IntNormType or DateFloorNormType. These will automatically normalize the range bounds to be inclusive. By default, ranges can be both open or closed, like the half-open interval [0,3) that got output in the example above. If we instead used IntNormType, this would get automatically normalized to [0,2] instead. This can be simpler to work with, and can improve performance.

There is no normalization for RealType, since there is no "next real number" you can modify to. You can use the FloatNormType however, albeit with negative performance impact, to normalize to the next representable floating point number.

Caution: The Norm types should not be passed pre-constructed ranges when constructing a RangeGroup. For optimization, it is assumed preconstructed ranges are already normalized. Pass arguments instead if you wish to have them normalized on creation (see API for options).

Custom Types

A design choice for the library was to decouple the Range and RangeType interfaces. This allows Range to be a plain JSON object, with operations on those objects described by RangeType. To create a new type, simply create an object with methods matching the RangeType interface. The methods provided in CommonType can provide a starting place, or you might wrap any of the other builtin types like IntType.

Additionally there are helpers like CommonType.compareEpsilon. It can wrap a type and define a threshold to merge two ranges:

const EpsilonType = CommonType.compareEpsilon(0.25, RealType)
const group = new RangeGroup(
	[[0,.1],[.3,.6]],
	{type:EpsilonType, normalize:true}
);
group.ranges; // {start:0, end:.6}

There is also CommonType.compareBinarySearch, which forces the type to use binary search instead of interpolation search. Binary search has better worst case time complexity, and a little less overhead, so can be a better choice in some scenarios.

Method Reference

The following methods are available on a RangeGroup:

General

• copy
• sort
• normalize: a combination of sort and selfUnion

Set iteration

• iterate, @@iterator

Set membership

• contains or has
• search: provides extra context about the found location

Set modification

• diff
• clear, toCleared
• filter, toFiltered, hasFilter
• union or add, toUnioned, hasUnion
• selfUnion, toSelfUnioned, hasSelfUnion
• difference or subtract or delete, toDifferenced, hasDifference
• intersect, toIntersected, hasIntersection
• symmetricDifference, toSymmetricDifferenced, hasSymmetricDifference

You'll notice there are three variants for many:

1. The modify methods perform the operation in-place
2. The toModified methods perform the operation on a copy, following the naming syntax introduced in ECMAScript 2023
3. The hasModification methods give a boolean whether the result would be non-empty, without actually calculating the full results.

Most the operations are implemented using the diff method. It supports numerous options, like customizing in-place vs copy, boolean results, filtering, and labeling the source RangeGroup. You can use the diff calculate additional operations that have not been given aliases.

Set characteristics

• isEqual: deep equality check
• isEmpty, cardinality or size,
• isProperSubset or isStrictSubset, isSubset
• isProperSuperset or isStrictSuperset, isSuperset